1. Field of the Invention
The present invention relates to a surface mounting device-type light emitting diode (hereinafter, referred to as an SMD-type LED) which maximizes efficiency of phosphor such that extraction efficiency of light to be emitted into a lens can be enhanced.
2. Description of the Related Art
Generally, a light emitting diode (hereinafter, referred to as ‘LED’) has light sources provided by varying compound semiconductor materials such as GaAs, AlGaAs, GaN, InGaInP and the like, thereby implementing various colors of light.
Recently, as the semiconductor technology rapidly develops, the production of LEDs with high luminance and high quality has become possible. Further, as the implementing of blue and white diodes with an excellent characteristic is realized, the use of LED is expanded into display devices, next-generation lighting sources and the like. For example, SMD-type LEDs are productized.
Now, a conventional SMD-type LED will be described in detail with reference to FIGS. 1 and 2.
FIG. 1 is a schematic view illustrating the structure of a general SMD-type LED. The SMD-type LED includes a package 20 formed of molding epoxy resin or the like. On a predetermined surface of the package 20, a light-emission window is opened so that light is easily emitted therethrough. On the light-emission window, a lens 90 having a convex upper surface is formed. On another surface of the package 20, a portion of a lead frame 50 is formed to project, the lead frame 50 being composed of one or more pairs of lead electrodes. The lead frame 50 is mounted on external circuits such as a printed circuit board and the like. Further, inside the package 20 constructed in such a manner, an LED chip (not shown) is disposed so that the light-emission surface thereof is directed toward the lens 90. The lead frame 50 and the LED chip are electrically connected through a wire (not shown).
FIG. 2 is a sectional view taken along I-I′ line of FIG. 1, showing the structure of the conventional SMD-type LED in detail.
As shown in FIG. 2, the SMD-type LED includes the lead frame 50 composed of one or more pairs of lead electrodes, the package 20 formed to house a portion of the lead frame 50 therein, the LED chip 60 mounted on the lead frame 50 inside the package 20, the wire 70 for electrically connecting the LED 60 an the lead frame 50, a phosphor-mixed layer 80 filled in the package 20 so as to protect the LED chip 60 and the wire 70 and to determine a color of light emitted from the LED chip 60, and the lens 90 formed on the package 20, the lens 90 coming in contact with the upper surface of the phosphor-mixed layer 80.
General standards for determining characteristics of LED chips include color, luminance, an intensity range of luminance and the like. Such characteristics are primarily determined by materials of compound semiconductors to be used in LED chips, but are incidentally influenced by the structure of a package for mounting an LED chip and a phosphor-mixed layer filled in the package. Particularly, the phosphor-mixed layer filled in the package has a large effect on the distribution of luminance.
However, the phosphor-mixed layer of the conventional SMD-type LED is filled in the entire package having the LED chip mounted therein. Therefore, the phosphor-mixed layer is formed at a relatively-large thickness, depending on the depth of the package.
When the phosphor-mixed layer has a large thickness as described above, the energy of light to be emitted from the LED chip is significantly reduced, while the light passes through the phosphor-mixed layer. As a result, light extraction efficiency decreases.
Further, in the conventional SMD-type LED, the phosphor-mixed layer is filled in the entire package. Therefore, a consumed amount of phosphor is so excessive that a manufacturing cost increases. Accordingly, a production yield decreases.